1. Field of the Invention
The present invention relates to a vehicle power transmission device, and, more particularly, to a technique of suppressing rattling of a planetary gear device included in the power transmission device.
2. Description of the Related Art
Conventionally, a planetary gear device is included in a vehicle power transmission device including an automatic transmission, a power distribution mechanism of a hybrid vehicle, etc., and power output from a drive source is output to a drive wheel via the planetary gear device. Such a planetary gear device may have a carrier that is brought into spline fitting with a case that is a non-rotating member to constantly stop the rotation of the carrier. One example is a support structure of a rotating member of Japanese Laid-Open Patent Publication No. 2005-308094, for example. Japanese Laid-Open Patent Publication No. 2005-308094 discloses the structure having a carrier of a planetary gear device in spline fitting with a case and discloses a technique of suppressing noise generated in the structure. Specifically, if the carrier of the planetary gear device is in spline fitting with the case, a gap (play) is formed in the thrust direction and the circumferential direction between the carrier and the case and, when rotational fluctuations transmitted from a drive source are transmitted to the carrier, the carrier and the case repeatedly collide in the thrust direction and the circumferential direction due to the rotational fluctuations and the collides (rattling) are transmitted as noise through the case to a driver. On the other hand, Japanese Laid-Open Patent Publication No. 2005-308094 describes that the generation of noise is suppressed by restricting the location of the spline fitting of the carrier and the case to a location with relatively low sensitivity to the noise (a location with relatively high rigidity) in the circumferential direction of the case.
However, a structure described in Japanese Laid-Open Patent Publication No. 2005-308094 does not constrain collision of a carrier and a case (rattling) and is not necessarily a sufficient solution of the problem. Therefore, a technique has been requested that constrains the rattling itself. On the other hand, a technique is also conceivable that constrains the rattling through control. Specifically, in a range tending to generate the rattling, an operating point of the drive source is changed to an operating point that constrains the occurrence of the rattling. However, when the rattling is suppressed through the control, the operating point of the drive source (engine) for avoiding the rattling deviates from an operating point for optimum fuel cost as depicted in FIG. 9, it is problematic that a fuel cost performance of vehicle deteriorates. As depicted in FIG. 9, it is also problematically difficult to generate sufficient power in a lower rotation speed range of the drive source. Therefore, the rattling constraint through the control is not certainly a means of preferably suppressing the rattling since the fuel cost deterioration and the insufficient drive force are problematically generated while the rattling is suppressed.